C＃从数据库显示图像

Question

I am having some issues displaying an image from a SQL Server database in a .NET application using C#. I've got the save part of the image working and it is storing the image as a series of byes in the database, but now I am running into issues trying to display it. Here is what I have:

using System;
using System.Configuration;
using System.Web;
using System.IO;
using System.Data;
using System.Data.SqlClient;

public class ShowImage : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        Int32 empno;
        if (context.Request.QueryString["id"] != null)
            empno = Convert.ToInt32(context.Request.QueryString["id"]);
        else
            throw new ArgumentException("No parameter specified");

        context.Response.ContentType = "image/jpeg";
        Stream strm = ShowEmpImage(empno);
        byte[] buffer = new byte[4096];
        int byteSeq = strm.Read(buffer, 0, 4096);

        while (byteSeq > 0)
        {
            context.Response.OutputStream.Write(buffer, 0, byteSeq);
            byteSeq = strm.Read(buffer, 0, 4096);
        }
        //context.Response.BinaryWrite(buffer);
    }

    public Stream ShowEmpImage(int empno)
    {
        string conn = CodProbs.Main.GetDSN();
        SqlConnection connection = new SqlConnection(conn);
        string sql = "SELECT CoverPhoto FROM Galleries WHERE GalleryID = @GalleryID";
        SqlCommand cmd = new SqlCommand(sql, connection);
        cmd.CommandType = CommandType.Text;
        cmd.Parameters.AddWithValue("@GalleryID", empno);
        connection.Open();
        byte[] img =                                                                   System.Text.Encoding.Unicode.GetBytes(Convert.ToString(cmd.ExecuteScalar()));
    try
    {
        return new MemoryStream((byte[])img);
    }
    catch
    {
        return null;
    }
    finally
    {
        connection.Close();
    }
}

public bool IsReusable
{
    get
    {
        return false;
    }
}

This is not resulting in any syntax errors and seems like it should be working. After stepping through it with the debugger, I can see that it is grabbing the proper data from the database. However, I receive an error of: "The image ... cannot be displayed because it contains errors."

Any ideas on what the issue is here?

UPDATE Storing the image

public static int AddGallery(GalleryDS galleryDS)
        {
            DataRow gallery = galleryDS.Tables[0].Rows[0];
            int result = 0;
            string sql = @"insert into Galleries (Title, Description,     GalleryCategoryID, CreateDate, CreatedBy, CoverPhoto)
                        values (@Title, @Description, @GalleryCategoryID, @CreateDate, @CreatedBy, @CoverPhoto)
                        select scope_identity()";

        using (SqlConnection conn = new SqlConnection(Main.GetDSN()))
        {
            SqlCommand command = new SqlCommand(sql, conn);
            command.Parameters.AddWithValue("@Title", gallery["Title"]);
            command.Parameters.AddWithValue("@Description", gallery["Description"]);
            command.Parameters.AddWithValue("@GalleryCategoryID", 0);
            command.Parameters.AddWithValue("@CreateDate", DateTime.Now);
            command.Parameters.AddWithValue("@CreatedBy", gallery["CreatedBy"]);
            command.Parameters.Add("@CoverPhoto", SqlDbType.VarBinary, Int32.MaxValue);
            command.Parameters["@CoverPhoto"].Value = gallery["CoverPhoto"];
            conn.Open();
            result = Convert.ToInt32(command.ExecuteScalar());
            conn.Close();
        }
        return result;
    }

Answer 1

The ShowEmpImage method shouldn't convert it to a stream and then write it. That's a waste of time.

Change the definition to:

public Byte[] ShowEmpImage(int empno) {
    string sql = "SELECT CoverPhoto FROM Galleries WHERE GalleryID = @GalleryID";
    Byte[] result = null;

    using (SqlConnection conn = new SqlConnection(CodProbs.Main.GetDSN())) {
        using(SqlCommand cmd = new SqlCommand(sql, conn)) {
            cmd.CommandType = CommandType.Text;
            cmd.Parameters.AddWithValue("@GalleryID", empno);
            conn.Open();
            result = (Byte[])cmd.ExecuteScalar();
        }
    }

    return result;
}

To call it use the following:

    Byte[] empImage = null;
    empImage = ShowEmpImage(empno);
    context.Response.Buffer = true;
    context.Response.Clear();
    context.Response.ContentType = "image/jpeg";
    context.Response.Expires = 0;
    context.Response.AddHeader("Content-Disposition", "attachment;filename=yourimagename.jpg");
    context.Response.AddHeader("Content-Length", empImage.Length.ToString());
    context.Response.BinaryWrite(empImage);

Side note: ALWAYS wrap unmanaged objects with the using clause. It cleans up after you and is simply good practice. Especially for database connections.